By simultaneously charging a pair of capacitors from the same low voltage level to the same high reference voltage level, the two charge time durations will be functions of and will be proportional to the capacitances of the two capacitors. A comparison of those charge time durations will thus provide an indication of the ratio of the capacitances of the two capacitors. This is achieved by including, in the measuring system, an oscillating circuit whose frequency is determined by the capacitance of one of the capacitors. A periodically-recurring rectangular wave is then developed having pulse components with pulse widths determined by the capacitance of the other capacitor, the frequency of the rectangular wave being equal to the oscillating frequency. The duty cycle of the rectangular wave is therefore proportional to and respresents the ratio of the capacitances of te capacitors. By averaging the rectangular wave in a low-pass filter, an output signal is produced having an amplitude which is proportional to and represents the capacitance ratio.